Agreed, chiffon can be a real headache --- particularly when you need relatively quick and easy.
Maybe you can talk them into something else. However, iIf they have fallen in love with the blinged-out chiffon, one simple way to use it is as an overskirt with a straight bottom. Make the underskirt with the scalloped edges, using a less expensive and easier-to-work-with coordinating fabric. You could even do the overskirt as a separate garment --- like an apron.
For the overskirt, cut a rectangle of the chiffon fabric. The width should be enough to gather with a nice amount of fullness. You probaby can just use the full width of your fabric as the width of your cut piece --- depends on the width of the fabric, and depends on the girls' waist measurements. For chiffon, you probably want at least 2 times fullness. Cut the length to be DOUBLE the skirt length (plus seam allowances, if you want to be precise) --- it can be thigh-length --- knee-length --- it doesn't have to be as long as the underskirt. Fold the piece in half --- right sides together ---- aligning one long edge with the other long edge. Sew/serge the SHORT sides. Turn right side out. Don't even try to press the seams or the bottom edge. The unpressed bottom edge will add to the flowiness of the skirt. Again, align the long edges together, this time with the wrong sides together. Gather the top edge in whatever way you prefer. At this point, you can put this skirt with the underskirt to attach it into the garment. OR you can attach some sort of waistband (ribbon, fabric, whatever), and you can either tie or velcro in the back.
So, if you're making each skirt to be 18" long, then you'll likely need 1 yard for each skirt. To keep your cutting simple and your yardage minimal, I would just try to use the full width of the fabric for the width of the skirt.
You can do this same style of overskirt using tulle. Of course, it will hang differently than chiffon, but it will be pretty.
If you use the special piece of fabric as an accent, the eye will be drawn there, and you can use any sort of coordinating fabric for the body of the dress. If you want something shiny, you could use a polyester satin. It's sorta slippery, too, and will ravel --- but it's not as difficult as chiffon. Look at some of the fabrics that are sold as garment lining fabrics. They usually come in nice colors and might have a sheen to them. Just take care that it's not too see-through -- or have the girls wear leotards underneath.
Good Luck
I just remembered one time when I used gold lame and I swore I would never use it again!!!
